Problem: The country of Freedonia has decided to reduce its carbon-dioxide emission by $35\%$ each year. This year the country emitted $40$ million tons of carbon-dioxide. Write a function that gives Freedonia's carbon-dioxide emissions in million tons, $E(t)$, $t$ years from today. $E(t)=$
Decreasing at a rate of $35\%$ per year means the emission keeps $100\%-35\%=65\%$ of its size each year. So each year, the emission is multiplied by $65\%$, which is the same as a factor of $0.65$. If we start with the initial emission, $40$ million tons, and keep multiplying by $0.65$, this function gives us Freedonia's carbon-dioxide emissions $t$ years from today: $E(t)=40(0.65)^t$